1. Field of the Invention
The present invention relates to a method of bump formation and more specifically to a method of IC chip bump formation performing the flip chip bonding.
2. Description of the Prior Art
Conventionally, the metal plating method is generally used in order to form bumps o aluminum electrodes for IC chips. However, as is shown FIG. 7, a bump 32 formed on an IC chip 31 using metal plating is plateau-shaped and the height-h is usually not more than 15 .mu.m.
When the flip chip bonding is used to install IC chips directly on bases, the difference between those materials may cause cracks in the joint part because of a stress concentration therein due to the differential thermal expansion coefficiences for temperature changes and may result a major cause of malfunctions due to disconnections.
In order to solve the above-mentioned problem, tall bumps are formed so as to absorb the differences of thermal expansion by deformation of the bumps, but in this method it is necessary to form bumps with a height of at least 50 .mu.m.
However, the prior art has not given a method to form bumps having a preferable height without dispersions with a low cost.
Taking the above-mentioned conventional problem into consideration, the object of the present invention is to provide a method for bump formation which can form bumps having a preferable height without dispersions with a low cost.